Definitions of sea ice climatic charts

Median of Ice Concentration

The "Median of Ice Concentration" charts consider total concentration of ice throughout the course of a year. The charts do not represent any real ice season but rather a statistical composite of all available seasons.

The charts represent the statistical "normal" ice concentration for the appropriate date. There is a high level of confidence throughout this atlas series.

Median of Predominant Ice Type When Ice Is Present

The "Median of Predominant Ice Type When Ice Is Present" charts consider the predominant ice type (ice type of the greatest concentration) throughout the course of a year.

The charts involve more interpretation than any of the remaining ice charts. The most appropriate way to interpret the charts is to view the median of predominant ice type in conjunction with the frequency of presence of sea ice chart. For example, at a particular point, the frequency of presence of sea ice might be in the range of 34-50% and the median of predominant ice type when ice is present might be first-year ice. Thus, at the point, there is a 34-50% chance of encountering sea ice, and when ice is present, it is "normally" first-year ice.

The charts represent the statistical "normal" predominant ice type when ice is present for the appropriate date. The level of confidence is generally high except in extreme areas where only a few occurrences of ice are found for a chart date.

Frequency of Presence of Sea Ice (%)

The "Frequency of Presence of Sea Ice (%)" charts consider the likelihood of total concentration of ice greater than or equal to 1/10 throughout the course of a year and are anticipated to give the reader an idea of the likelihood that ice will occur at a particular location for the appropriate date.

The charts can be interpreted as the "odds of encountering sea ice for the dataset". The charts depict above normal extent (1 to 33%), near normal extent (34 to 66%) and below normal extent (67 to 99%). The 0% line represents the maximum extent of sea ice, beyond it no ice was reported in the dataset; the 100% line represents the minimum extent of sea ice, within it there has always been ice reported in the dataset. There is a high level of confidence throughout this atlas series.

Median of Old Ice Concentration

The "Median of Old Ice Concentration" charts consider the concentration of old ice throughout the course of a year. The charts do not represent any real ice season but rather a statistical composite of all available seasons.

The charts represent the statistical "normal" concentration of old ice for the appropriate date. The level of confidence is not as high as the median of total ice but we believe that most of the errors in old ice affecting this product have been corrected.

Frequency of Presence of Old Ice: 1 to 10/10 (%)

The "Frequency of Presence of Old Ice: 1 to 10/10 (%)" charts consider the likelihood of old ice greater than or equal to 1/10 throughout the course of a year and are anticipated to give the reader an idea of the likelihood that old ice will occur at a particular location for the appropriate date.

The charts can be interpreted as the "odds of encountering old ice in concentration of 1/10 or more for the dataset". The charts depict above normal extent (1 to 33%), near normal extent (34 to 66%) and below normal extent (67 to 99%). The 0% line represents the maximum extent of old ice, beyond it no old ice was reported in the dataset; the 100% line represents the minimum extent of old ice, within it there has always been old ice of concentration of 1/10 or more reported in the dataset.

The level of confidence is generally good but is lower in areas of low frequency and high ice mobility and dispersion such as Foxe Basin, Hudson strait and North Hudson Bay.

Frequency of Presence of Old Ice: 4 to 10/10 (%)

The "Frequency of Presence of Old Ice: 4 to 10/10 (%)" charts consider the likelihood of old ice greater than or equal to 4/10 throughout the course of a year and are anticipated to give the reader an idea of the likelihood that old ice greater than or equal to 4/10 will occur at a particular location for the appropriate date.

The charts can be interpreted as the "odds of encountering old greater than or equal to 4/10 for the dataset". The charts depict above normal extent (1 to 33%), near normal extent (34 to 66%) and below normal extent (67 to 99%). The 0% line represents the maximum extent of 4/10 or greater old ice, beyond it no 4/10 or greater old ice was reported in the dataset; the 100% line represents the minimum extent of 4/10 or greater old ice, within it there has always been 4/10 or greater old ice reported in the dataset.

The level of confidence is generally good and better than the above product in areas of low frequency and high ice mobility and dispersion such as Foxe Basin, Hudson strait and North Hudson Bay.

Median of Ice Concentration When Ice is Present

The "Median of Ice Concentration When Ice is Present" charts consider total concentration of ice on a weekly period from November 12 to August 27.

The charts are a new addition to the atlas and are meant to assist in interpreting the complementary "Median of Predominant Ice Type When Ice Is Present" charts. The most appropriate way to interpret the charts is to view the median of ice concentration when ice is present in conjunction with the frequency of presence of sea ice charts. For example, at a particular point, the frequency of presence of sea ice might be in the range of 34-50% and the median of ice concentration when ice is present might be 9/10 to 9+/10. Thus, at this location, there is a 34-50% chance of encountering sea ice, and when ice is present, it is "normally" 9/10 to 9+/10 concentration. Additional insights may be provided by examining the "Predominant Ice Type When Ice Is Present" charts.

The charts represent the statistical "normal" ice concentration when ice is present for the appropriate date.

Dates of Freeze-up and Break-up

The "Dates of Freeze-up and Break-up" depicts the extent of ice on a bi-weekly basis during the freeze-up and break-up seasons. They provide a pictorial representation of the evolution of ice during those periods.

These products are constructed using the Median of Ice Concentration charts and thus the confidence level is high.